Determination apparatus for determining type of recording medium and image forming apparatus using the same

ABSTRACT

An apparatus for determining a type of a recording medium is provided. A detection unit detects a characteristic value indicating a physical characteristic of a recording medium. A measurement unit measures a moisture content correlated with a moisture content of the recording medium. A determination unit determines the type of the recording medium based on the moisture content and the characteristic value. The determination unit may correct the characteristic value using the moisture content or correct a rule for determining the type of the recording medium using the moisture content unit, and determines the type of the recording medium in accordance with the corrected characteristic value or the corrected rule.

This application is a continuation of U.S. application Ser. No.15/958,429, filed Apr. 20, 2018, which is a continuation of U.S.application Ser. No. 14/939,452, filed Nov. 12, 2015 (now issued as U.S.Pat. No. 9,983,530 on May 29, 2018), which claims priority to Japan2014-240367, filed on Nov. 27, 2014 the contents of which areincorporated herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a determination apparatus fordetermining the type of a recording medium and an image formingapparatus using the same.

Description of the Related Art

In order for an image forming apparatus to properly adjust a usageamount of toner or ink or properly reproduce a gradation characteristicof an original image, image forming conditions need to be adjusted inaccordance with characteristics (grammage, thickness, surface propertyand the like) of a recording medium. Japanese Patent Laid-Open No.2004-107030 proposes detecting the grammage (weight per unit of area) ofa recording medium using ultrasonic waves. Japanese Patent Laid-Open No.2002-182518 proposes detecting a surface property of a recording mediumusing a CMOS sensor.

If the type of a recording medium is detected using inventions describedin Japanese Patent Laid-Open No. 2004-107030 and Japanese PatentLaid-Open No. 2002-182518 and image forming conditions are adjusted inaccordance with the detected type, the image forming apparatus will beable to achieve an image quality of a certain level. However, in theinventions described in Japanese Patent Laid-Open No. 2004-107030 andJapanese Patent Laid-Open No. 2002-182518, variations in a detectionvalue due to the moisture content of a recording medium is notconsidered, and thus there is room for further improving detectionaccuracy for the type of a recording medium.

SUMMARY OF THE INVENTION

In view of this, the present invention improves detection accuracy forthe type of recording medium.

The present invention provides an apparatus for determining a type of arecording medium, comprising the following elements. A detection unit isconfigured to detect a characteristic value indicating a physicalcharacteristic of a recording medium. A measurement unit is configuredto measure a moisture content correlated with a moisture content of therecording medium. A determination unit is configured to determine thetype of the recording medium based on the moisture content measured bythe measurement unit and the characteristic value detected by thedetection unit. The determination unit is further configured to correctthe characteristic value detected by the detection unit using themoisture content measured by the measurement unit or corrects a rule fordetermining the type of the recording medium using the moisture contentmeasured by the measurement unit, and determine the type of therecording medium in accordance with the corrected characteristic valueor the corrected rule.

The present invention further provides an image forming apparatuscomprising the following elements. An image forming unit is configuredto form an image on a recording medium. A detection unit is configuredto detect a characteristic value indicating a physical characteristic ofthe recording medium. A measurement unit is configured to measure amoisture content correlated with a moisture content of the recordingmedium. A determination unit is configured to determine an image formingcondition of the image forming unit based on the moisture contentmeasured by the measurement unit and the characteristic value detectedby the detection unit. The determination unit is further configured tocorrect the characteristic value detected by the detection unit usingthe moisture content measured by the measurement unit or corrects a rulefor determining the image forming condition using the moisture contentmeasured by the measurement unit, and determine the image formingcondition in accordance with the corrected characteristic value or thecorrected rule.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing functions of an image formingapparatus.

FIG. 2 is a diagram showing an example of a configuration of an imageforming apparatus.

FIG. 3 is a block diagram showing functions of a determinationapparatus.

FIG. 4 is a diagram showing an example of a variation rate of a moisturecontent and a characteristic value.

FIG. 5 is a flowchart showing a recording medium determination method.

FIG. 6 is a diagram showing an example of a variation rate of a moisturecontent and a characteristic value.

FIG. 7 is a flowchart showing a recording medium determination method.

FIG. 8 is a block diagram showing functions of a determinationapparatus.

FIG. 9 is a diagram showing an example of a variation rate of a moisturecontent and a characteristic value.

FIG. 10 is a flowchart showing a recording medium determination method.

FIG. 11 is a diagram showing an example of a variation rate of amoisture content and a characteristic value.

FIG. 12 is a flowchart showing a recording medium determination method.

FIG. 13 is a diagram showing an example of a configuration of an imageforming apparatus.

DESCRIPTION OF THE EMBODIMENTS

A technical idea of embodiments of the present invention will bedescribed with reference to FIG. 1. In FIG. 1, an image formingapparatus 1 is provided with an image forming unit 50 for forming animage using ink or toner. A determination apparatus 30 determines thetype of a recording medium on which an image is to be formed by theimage forming unit 50. The type of a recording medium includes plainpaper, thick paper, thin paper, coated paper, bond paper and the like.The determination apparatus 30 has a measurement unit 22 for measuring amoisture content correlated to a moisture content of a recording medium,a detection unit 23 for detecting a characteristic value indicating aphysical characteristic of the recording medium, and a determinationunit 24 for determining the type of the recording medium based on themoisture content and the characteristic value. The determination unit 24may have a correction unit 25 for correcting a characteristic value anda rule for determining the type of the recording medium in accordancewith a moisture content. The determination unit 24 determines the typeof the recording medium in accordance with the characteristic value orthe rule corrected by the correction unit 25. The physicalcharacteristic of a recording medium includes the grammage and thesurface property of the recording medium, for example, and is aparameter that influences image forming conditions. The grammage and thesurface property of a recording medium change in accordance with themoisture content contained in the recording medium. Therefore, under anenvironment in which this moisture content deviates from a moisturecontent that was envisioned in advance, determination accuracy for thetype of the recording medium can deteriorate. Therefore, in thisembodiment, the correction unit 25 corrects a characteristic valueoutput from the detection unit 23 and the rule for determining the typeof the recording medium in accordance with the moisture contentcontained in the recording medium, thereby improving the determinationaccuracy for the type of the recording medium. The rule for determiningthe type of the recording medium is a rule for comparing one or morethresholds and the characteristic value and determining the type inaccordance with the comparison result, for example. Therefore,correcting the rule includes correcting the threshold. By taking themoisture content of a recording medium into consideration in thismanner, detection accuracy for the type of the recording mediumimproves. Note that the moisture content of the recording medium may bedirectly measured, but indirect measurement can make the configurationof the measurement unit 22 simpler. Commonly, the moisture content of arecording medium is correlated with the moisture content of the spacearound the recording medium. Therefore, it is sufficient that themeasurement unit 22 measures the moisture content around the recordingmedium. However, unless the measurement unit 22 is separated from a heatsource such as a fixing apparatus by a predetermined distance or more,the measurement unit 22 erroneously detects the moisture content due tothe influence of the heat source. In particular, the measurement unit 22that detects the temperature and the humidity and calculates a moisturecontent is likely to be influenced by a heat source. In the case wherethe measurement unit 22 cannot be arranged near the recording medium,the measurement unit 22 is at least arranged at a position away from aheat source. For example, the measurement unit 22 may be arranged on aconveyance path that is away from a main heat source by a predetermineddistance or more, in a housing unit for accommodating a recordingmedium, or the like. It is not necessary for the measurement unit 22 tobe mounted directly on the conveyance path or the housing unit, and itis sufficient that it is arranged around the conveyance path or thehousing unit.

First Embodiment

The image forming apparatus 1 will be described with reference to FIG.2. Here, an electrophotographic method is adopted as an image formingmethod of the image forming apparatus 1, but an electrostatic recordingmethod, an ink jet recording method or the like may be adopted.Moreover, the image forming apparatus 1 is described as forming amulticolor image, but may be an image forming apparatus for forming asingle-color image.

The image forming apparatus 1 is a tandem type color laser beam printerand outputs a multicolor image by superimposing images of a plurality ofdeveloping agents with different colors. The developing agents are fourcolor toners, for example, yellow (Y), magenta (M), cyan (C), and black(K). A feeding cassette 2 is an example of a feeding unit andaccommodates a recording medium P. A conveyance apparatus is provided ona conveyance path for the recording medium P. The conveyance apparatusis provided with a pair of conveyance rollers 5 and 6 for conveying therecording medium P fed from a feeding roller 4 for feeding the recordingmedium P from the feeding cassette 2, or from the feeding cassette 2. Aphotoreceptor drum 11 is an image carrier for carrying an electrostaticlatent image and a toner image. A charging roller 12 is a charging unitfor uniformly charging the surface of the photoreceptor drum 11 to apredetermined potential. A laser scanner 13 is an exposure apparatus oran optical scanning apparatus that irradiates the surface of thephotoreceptor drum 11 with light in accordance with an image signal toform an electrostatic latent image. A process cartridge 14 has adeveloping roller 15. The developing roller 15 is a developing unit thatdevelops an electrostatic latent image formed on the photoreceptor drum11 using toner to visualize the image. A primary transfer roller 16 is atransfer unit for primarily transferring a toner image formed on thephotoreceptor drum 11 to an intermediate transfer belt 17. Theintermediate transfer belt 17 is an intermediate transfer member that isdriven by a driving roller 18 and conveys a toner image transferred fromthe photoreceptor drum 11. A secondary transfer roller 19 is a transferunit for transferring a toner image formed on the intermediate transferbelt 17 to the recording medium P. A fixing apparatus 20 is a unit formelting and fixing a toner image transferred to the recording medium Pwhile conveying the recording medium P.

Arrangement and Configuration of Determination Apparatus

As shown in FIG. 2, the determination apparatus 30 is provided on theconveyance path for a recording medium P. The main heat source in theimage forming apparatus 1 is the fixing apparatus 20, and themeasurement unit 22 for measuring the moisture content is arranged at aposition separated from the fixing apparatus 20. A control unit 10functions as the above-described determination unit 24, and alsofunctions as a decision unit 26. Moreover, the control unit 10 may beprovided with a calculation function, a signal processing function andthe like of the measurement unit 22 and the detection unit 23.

The determination apparatus 30 for detecting the grammage of therecording medium P and determining the type of the recording medium Pwill be described with reference to FIG. 3. In this embodiment, as amethod for determining the grammage, a method is adopted in which therecording medium P is irradiated with ultrasonic waves, the ultrasonicwaves transmitted through the recording medium P are received, and atype is determined based on the amplitude of the reception signal.

The detection unit 23 functions as a grammage detection unit fordetecting the grammage of the recording medium P conveyed thereto. Thedetection unit 23 has a transmission unit 31 and a reception unit 32.For example, the control unit 10 is constituted by an MPU (notillustrated) provided with a CPU, a memory, and the like, and executescontrol of the detection unit 23 and calculation processing for ameasurement result of the measurement unit 22. Moreover, the controlunit 10 integrally controls the units of the image forming apparatus 1.

The measurement unit 22 detects a temperature and a relative humidity asparameters indicating a moisture content using a temperature andhumidity sensor 40, and outputs the temperature and the relativehumidity to the control unit 10. The control unit 10 determines an imageforming condition (print mode) in accordance with the type of therecording medium P, based on a measurement result of the measurementunit 22 and a detection value of the detection unit 23. The control unit10 performs collective control of an electrophotographic process inaddition to control of the detection unit 23 and the measurement unit 22and processing of a detection result, but an independent control unitmay be provided for these processes. For example, a first control unitfor performing control of the detection unit 23 and the measurement unit22 and processing of a detection result, and a second control unit forperforming control of the electrophotographic process may be provided sothat the first control unit and the second control unit communicate toshare information. Moreover, a first control unit for performing controlof the detection unit 23 and a second control unit for performingprocessing of a measurement result of the measurement unit 22 andcontrol of the electrophotographic process may be provided such that thefirst control unit and the second control unit communicate to shareinformation.

The measurement unit 22 detects a temperature and a humidity using thetemperature and humidity sensor 40, so as to indirectly measure amoisture content. In this embodiment, the temperature and humiditysensor 40 is used, but a sensor other than the temperature and humiditysensor 40 may be used as long as the sensor is an environment sensorcapable of detecting an environment parameter that enables a moisturecontent to be obtained. The temperature and humidity sensor 40 isarranged in a place that is near the exterior of the image formingapparatus 1 and is unlikely to be influenced by a heat source in theimage forming apparatus 1 so that the temperature and the humidity nearthe image forming apparatus 1 can be detected. However, it is sufficientthat the temperature and the humidity near the image forming apparatus 1can be detected, and therefore the arrangement place is not limitedthereto. The measurement unit 22 may obtain the moisture content nearthe image forming apparatus 1 from a detection result of the temperatureand humidity sensor 40 using a conversion table or a function set basedon correlation data between the temperature and the humidity near theimage forming apparatus 1 and the detection result of the temperatureand humidity sensor 40 in the image forming apparatus 1. Note that aconversion function (from the temperature and the humidity) into amoisture content may be provided in the measurement unit 22 or in thecontrol unit 10.

The detection unit 23 has the transmission unit 31 for transmittingultrasonic waves and the reception unit 32 for receiving ultrasonicwaves. When the recording medium P is conveyed between the transmissionunit 31 and the reception unit 32, the control unit 10 instructs atransmission control unit 42 to perform an operation start. Uponreceiving the instruction of the operation start, the transmissioncontrol unit 42 generates a drive signal for transmitting ultrasonicwaves of a specific frequency and supplies the drive signal to thetransmission unit 31. The transmission unit 31 is driven by the drivesignal, generates ultrasonic waves of a specific frequency, andtransmits the ultrasonic waves toward the recording medium P. Thereception unit 32 receives the ultrasonic waves transmitted through therecording medium P and outputs a reception signal. A reception detectionunit 43 outputs the peak value of the amplitude of the reception signalas a detection voltage to an AD port of the control unit 10. The controlunit 10 receives the output from the reception detection unit 43 usingthe AD port. The AD port of the control unit 10 converts the detectionvoltage into a digital detection value (dec value) (both the analogdetection voltage and the digital detection value are parameterscorrelated with a characteristic value). For example, the AD portgenerates a dec value with a resolution of 256 levels based on a powersupply voltage input to the control unit 10. More specifically, the ADport converts the detection voltage into the dec value so as to indicatethe proportion of the input detection voltage with respect to theresolution. For example, if the power supply voltage of the control unit10 is 3.3 V and the detection voltage input to the AD port is 1.65 V,the AD port outputs 128 as the dec value. In this embodiment, the decvalue was described as being expressed in 256 levels, but thisresolution is merely an example.

Upon receiving a detection voltage (when generating a dec value), thecontrol unit 10 instructs an operation stop of the transmission controlunit 42. The transmission control unit 42 stops generation of the drivesignal in accordance with the instruction of the operation stop. Thisstops transmission of ultrasonic waves. A sheet sensor may be used. Thecontrol unit 10 causes ultrasonic waves to be transmitted when a sheetis passing by the detection unit 23, and stops transmission ofultrasonic waves when a sheet is not passing by the detection unit 23.This makes it possible to achieve power consumption reduction and noisereduction.

The attenuation amount of ultrasonic waves transmitted through therecording medium P is proportional to the grammage of the recordingmedium P. That is, the larger the grammage of the recording medium P is,the larger the attenuation amount of ultrasonic waves is. In the case ofa recording medium P with a small grammage (thin paper), the attenuationamount of ultrasonic waves is small, and the peak value of the receptionsignal and the dec value are large. Conversely, in the case of arecording medium P with a large grammage (thick paper), the attenuationamount of ultrasonic waves is large, and the peak value and the decvalue are small. For example, in the case where the dec value is large,the determination unit 24 determines that the type of the recordingmedium P is thin paper. Moreover, in the case where the dec value issmall, the determination unit 24 determines that the type of therecording medium P is thick paper. Commonly, the grammage of plain paperis less than or equal to 115 g/m², while the grammage of coated paperexceeds 115 g/m². For example, assume that the dec value obtained by thedetection unit 23 detecting a recording medium P having a grammage of115 g/m² is 90 dec. In this case, the determination unit 24 sets 90 decas a first threshold, and if the dec value exceeds the first threshold,determines that the recording medium P is plain paper. Moreover, if thedec value is less than or equal to the first threshold, thedetermination unit 24 may determine that the recording medium P iscoated paper. As an example, the type threshold is set to 90 dec, butthe type threshold can be freely set in accordance with the type that isdesired to be determined. In general, the grammage of thin paper isoften less than or equal to 70 g/m². Assume that the dec value obtainedby the detection unit 23 detecting a recording medium P with a grammageof 70 g/m² is 150 dec. In this case, the determination unit 24 sets 150dec as a second threshold, and if the dec value exceeds the secondthreshold, determines that the recording medium P is thin paper.Moreover, if the dec value is less than or equal to the second thresholdand exceeds the first threshold, the determination unit 24 may determinethat the recording medium P is plain paper. In this manner, with aplurality of type thresholds, determination of three types or more ispossible.

Type of Recording Medium and Image Forming Condition

In general, the electrical resistance value of the recording medium P isdifferent depending on the grammage of the recording medium P, andtherefore the decision unit 26 of the control unit 10 adjusts transferconditions such as the transfer current and the transfer voltagenecessary for transferring toner. Moreover, the thermal capacity isdifferent in accordance with the grammage of the recording medium P, andtherefore the decision unit 26 adjusts fixing conditions such as thefixing temperature and the fixing time for fixing toner and theconveyance speed of the recording medium P. The amount of heat thatpropagates to the toner and the recording medium P changes due toadjusting these fixing conditions. Therefore, the decision unit 26 setsimage forming conditions (the transfer conditions, the fixingconditions, and the like) applied to the image forming unit 50 inaccordance with the type of the recording medium P.

Moisture Content and Image Forming Conditions

The resistance value and the grammage of the recording medium P changein accordance with the moisture content. Therefore, the decision unit 26sets the image forming conditions in accordance with the resistancevalue and the grammage of the recording medium P in consideration of themoisture content. The change in the resistance value of the recordingmedium P in accordance with the moisture content differs depending onthe type of the recording medium P. That is, the decision unit 26 setsthe image forming conditions in accordance with the type and themoisture content of the recording medium P, so that a desired imagequality is achieved.

Influence of Moisture Content on Determination of Type of RecordingMedium

The influence that the moisture content has on determination of the typeof the recording medium P will be described. The grammage of therecording medium P changes due to the moisture content near therecording medium P. For example, if the moisture content is large, themoisture content contained in fibers composing the recording medium Pincreases, and thus the grammage of the recording medium P increases dueto the contained moisture content. On the other hand, if the moisturecontent is small, the moisture content contained in fibers composing therecording medium P decreases and thus the grammage decreases. Therefore,the moisture content near the recording medium P influencesdetermination of the type of the recording medium P. For example, thedetermination result of the recording medium P is sometimes differentbetween the case where the type of the recording medium P is determinedbased on the dec value of the grammage that has changed due to themoisture content and the case where the type of the recording medium Pis determined after the dec value of the grammage is converted into adec value under an environment with a specific moisture content. In viewof this, the correction unit 25 converts the dec value of the grammageinto a dec value in a specific environment and subsequently thedetermination unit 24 determines the type of the recording medium P sothat desired detection accuracy is achieved.

In this embodiment, as an example of the moisture content, an absolutemoisture content obtained based on the temperature and the humidity isused. The correction unit 25 executes conversion processing of the decvalue based on an environment in which the absolute moisture content isapproximately 11.5 g/m³ (corresponding to a temperature of 25 C and ahumidity of 50% RH). In this embodiment, the absolute moisture contentis used as an example, but it is sufficient that the moisture contentthat is correlated with the moisture content contained in the recordingmedium P is used, and the moisture content other than the absolutemoisture content, for example, a moisture content obtained based on arelative humidity may be used. For example, in the case of determiningthe type of the recording medium P within a temperature range in whichchange in moisture content is small, the moisture content contained inthe recording medium P may be estimated based on the relative humiditynear the recording medium P. In such a case, the moisture contentobtained based on the relative humidity has accuracy similar to that ofan absolute moisture content obtained based on the temperature and thehumidity.

Relation Between Moisture Content and Detection Result

Next, influence that variation in moisture content detected based on thedetection result of the temperature and humidity sensor 40 has on thedetection value of the detection unit 23 will be described withreference to inventors' experiment results shown in FIG. 4. As describedabove, in this embodiment, the absolute moisture content around therecording medium P is used in order to estimate the moisture contentcontained in the recording medium P. In FIG. 4, the horizontal axisindicates the absolute moisture content detected by the temperature andhumidity sensor 40. The vertical axis indicates the variation rate V ofthe dec value based on the dec value in an environment where theabsolute moisture content is approximately 11.5 g/m³ (corresponding to atemperature of 25 C and a humidity of 50% RH). Here, as an example,variation rates V for recording media P (plain paper) having grammagesof 60 g/m², 80 g/m², and 90 g/m² are shown. Measurement is executedafter each of the recording media P is sufficiently adapted to thetemperature and humidity environment.

Because the grammage increases/decreases in accordance withincrease/decrease in moisture content, the relation between the absolutemoisture content and the variation rate V of the dec value is linear asshown in FIG. 4. That is, it can be seen that the dec value of therecording medium P changes in proportion to the moisture content nearthe recording medium P. Therefore, by substituting the moisture contentin an approximation equation of the variation rate V obtained from FIG.4, the variation rate V of the dec value is determined. The correctionunit 25 then corrects or converts the dec value into a dec value under aspecific environment by dividing the dec value by the variation rate V.corrected dec value=dec value/variation rate V  Correction Equation 1As an example, as shown in FIG. 4, the dec value of the recording mediumP of grammage 60 g/m² under an environment in which the absolutemoisture content is 20 g/m³ is 1.022 times the dec value under anenvironment in which the absolute moisture content is 11.5 g/m³.Therefore, the correction unit 25 divides the dec value by 1.022 inorder to convert the dec value into the dec value under the specificenvironment in which the absolute moisture content is 11.5 g/m³. Thatis, the correction unit 25 divides the dec value by the variation rateV, so that the dec value is corrected to a dec value under a specificenvironment.

As for the three types of the recording media P (plain paper) shown inFIG. 4, it can be seen that variation in the variation rate V is smallregardless of the difference in grammage. Therefore, as for a pluralityof recording media P with small differences in grammage, the dec valuecan be accurately corrected even if the approximation equation is notchanged in accordance with the type of the recording medium P. In thecase of this embodiment, the correction unit 25 obtains the variationrate V of the dec value of the detection unit 23 by substituting themoisture content obtained by the temperature and humidity sensor 40 inthe following approximation equation 1. As described above, thecoefficient of the approximation equation 1 is determined based on thevariation rate V of the dec value for the absolute moisture content ofthe recording medium P having the grammage of 80 g/m² in FIG. 4.variation rate V=0.03×moisture content (g/m³)+0.98  Approximationequation 1Here, the approximation equation 1 of the variation rate V is an examplein this embodiment, and is appropriately set in accordance with thedetection characteristics of the detection unit 23. Moreover, in thisembodiment, the dec value is corrected based on the moisture contentobtained from the detection result of the temperature and humiditysensor 40. However, it is sufficient that the determination result forthe type of the recording medium P that is in accordance with themoisture content can be obtained, and the present invention is notlimited only to a method in which the dec value is corrected. Forexample, the target of correction does not need to be the dec value, andthe rule that is used for determining the type of the recording mediumP, that is, the type threshold for the dec value may be changed. Forexample, the correction unit 25 may increase/decrease 90 dec, which isthe type threshold for distinguishing between plain paper and coatedpaper, in accordance with the moisture content. Accordingly, detectionaccuracy for the type of the recording medium P that is in accordancewith the moisture content improves without correcting the dec value.Alternatively, a method other than the method in which the dec value orthe type threshold is corrected may be adopted. For example, thedetermination unit 24 may store, in a storage unit, a table indicatingthe relation between the moisture content near the recording medium Pand the dec value, and refer to the table based on the obtained moisturecontent and dec value and identify the type of the recording medium P.For example, a table, based on which it is determined that the type ofthe recording medium P is plain paper in the case where the moisturecontent is 11.5 g/m³ and the dec value corresponds to a grammage of 116g/m² and it is determined that the type of the recording medium P iscoated paper in the case where the moisture content is 5 g/m³ and thedec value corresponding to a grammage of 116 g/m², may be used.Moreover, the control unit 10 may control image forming conditions ofthe image forming apparatus 1 directly based on the corrected dec valuewithout determining the type of the recording medium P. Alternatively,the image forming conditions of the image forming apparatus 1 may becontrolled directly based on the dec value and the corrected rule. Forexample, the correspondence relation between the dec value or the likeand an image forming condition is stored in advance in a storageapparatus, so that an image forming condition is determined directlybased on the dec value or the like.

In this embodiment, the moisture content near the recording medium P ishandled as the same as the moisture content near the image formingapparatus 1. In general, the recording medium P is placed in the feedingcassette 2, a feeding tray, or an optional feeder. That is, therecording medium P is located in a place which is not significantlyinfluenced by a power supply apparatus within the image formingapparatus 1 or a heat source such as a driving source. Therefore, themoisture content near the recording medium P is considered substantiallythe same as the moisture content near the image forming apparatus 1. Inthis embodiment, the moisture content near the recording medium P wasobtained using the temperature and humidity sensor 40 for detecting themoisture content near the image forming apparatus 1. However, it issufficient that the moisture content near the recording medium P can beobtained, and the method for obtaining the moisture content is notlimited thereto. For example, the dedicated temperature and humiditysensor 40 may be arranged in the feeding cassette 2.

Flowchart

A method for determining the type of the recording medium P in thecontrol unit 10 will be described with reference to FIG. 5. In stepS501, the control unit 10 (the measurement unit 22 or the determinationunit 24) measures the moisture content related to the recording medium Pusing the temperature and humidity sensor 40. For example, the controlunit 10 obtains a measurement value of the temperature and a measurementvalue of the humidity from the temperature and humidity sensor 40, andconverts the measurement value of the temperature and the measurementvalue of the humidity into an absolute moisture content using a functionor a table.

In step S502, the control unit 10 (the determination unit 24 and thecorrection unit 25) calculates the variation rate V which is acorrection coefficient for correcting a characteristic value (e.g.,grammage). For example, the control unit 10 may calculate the variationrate V by substituting the moisture content in the above-describedapproximation equation 1.

In step S503, the control unit 10 starts transmission of ultrasonicwaves. As described above, the control unit 10 instructs thetransmission control unit 42 to start transmission of ultrasonic waves.This may involve sending out an ON signal to the transmission controlunit 42, for example. Note that transmission and stopping of ultrasonicwaves may be controlled by supplying or cutting off operation electricalpower for the transmission control unit 42 from a power supply.

In step S504, the control unit 10 executes ultrasonic wave receptionprocessing. For example, the ultrasonic waves transmitted through therecording medium P are received by the reception unit 32, and adetection voltage is generated by the reception detection unit 43 and isinput to the AD port of the control unit 10. The control unit 10 obtainsthe dec value, which is a characteristic value, by converting the analogdetection voltage into a digital dec value.

In step S505, the control unit 10 stops the transmission of ultrasonicwaves. The control unit 10 instructs the transmission control unit 42 tostop the transmission of ultrasonic waves as described above. This mayinvolve sending out an OFF signal to the transmission control unit 42 orstopping the sending out of an ON signal, for example.

In step S506, the control unit 10 (the correction unit 25) corrects thecharacteristic value. For example, the correction unit 25 corrects thedec value, which is a characteristic value, based on the variation rateV. Correction may be performed using a function, a table, or the like inwhich the variation rate V and the characteristic value serve as inputs,and the corrected characteristic value serves as the output. Forexample, the function may be a function that is used for outputting acorrected characteristic value by dividing the dec value, which is acharacteristic value, by the variation rate V.

In step S507, the control unit 10 (the determination unit 24) determinesthe type of the recording medium using the corrected characteristicvalue. For example, the determination unit 24 compares thecharacteristic value and one or more thresholds, and determines the typeof the recording medium. A plurality of thresholds are used in order todetermine three types or more.

In step S508, the control unit 10 (the decision unit 26) determines animage forming condition (e.g., transfer condition or fixing condition)that is in accordance with the type of the recording medium. Imageforming conditions that are in accordance with types of recording mediamay be prepared in advance, and the decision unit 26 may select an imageforming condition that is in accordance with the type of the recordingmedium from among the plurality of image forming conditions. Moreover,the decision unit 26 may also set image forming conditions in accordancewith the type of recording medium and the moisture content. For example,the decision unit 26 may determine an image forming condition that is inaccordance with the type of the recording medium and the moisturecontent by inputting the moisture content to a function or a table forobtaining an image forming condition prepared for each type of recordingmedium.

According to this embodiment, the determination apparatus 30 corrects acharacteristic value of a recording medium P (e.g., detection value ofgrammage) based on a moisture content obtained from the temperature andhumidity sensor 40, thereby improving detection accuracy for the type ofthe recording medium P. For example, it is possible to determine typesof recording media P having a grammage difference of approximately 10g/m² or less, for example, recording media P of grammages of 70 g/m² and80 g/m², which could not be clearly determined conventionally due tovariation caused by a moisture content. As a result, the apparatus 1provided with the determination apparatus 30 can appropriately set animage forming condition in accordance with the determined type of therecording medium P, and thus image quality can be improved. Furthermore,as an example of a method for obtaining an appropriate image formingcondition, the relation between an image forming condition and acombination of a moisture content and a detection value is stored in thecontrol unit 10. Furthermore, it is also possible to determine an imageforming condition without determining the type of the recording mediumP, by referring to the relation based on a combination of an obtainedmoisture content and detection value. Such a relation may be tabulated.

Second Embodiment

In the first embodiment, the variation rate V of the grammage of arecording medium P is obtained based on a moisture content obtained fromthe temperature and humidity sensor 40, and a detection value iscorrected based on the variation rate V. Note that the variation rate Vof the first embodiment is obtained in the same manner regardless of thetype of the recording medium P, thereby simplifying the calculation. Inthis embodiment, a method for determining a plurality of variation ratesV is prepared in advance so as to improve detection accuracy for aspecific type of a recording medium P such as coated paper. In a secondembodiment, descriptions of portions common with those in the firstembodiment are omitted for simplifying the description.

The type of the recording medium P used in the image forming apparatus 1is not limited only to a general recording medium P (plain paper)composed of pulp fibers, and a recording medium P whose surface has apigment applied thereto and has been subjected to smoothing processing(coated paper) is used in some cases. In particular, coated paper makesit possible to form a brightly colored image in multicolor printing, andopportunities for use have been increasing. If detection accuracy for aspecific type of a recording medium P such as the above-described coatedpaper can be improved, a more appropriate image forming condition willbe determined. In view of this, in this embodiment, correction of acharacteristic value in the case where the recording medium P is coatedpaper will be described as an example. Note that the specific type ofthe recording medium P is not limited to coated paper, and it is alsopossible to correct a characteristic value for thin paper as an example.

Relation Between Type of Recording Medium P and Detection Value ofGrammage

The influence on the detection value of the grammage in the case ofdifferent types of recording media P will be described with reference toFIG. 6. As described above, coated paper has a pigment applied to thesurface thereof. Therefore, the grammage of the recording medium P willtake a value that includes the grammage of the pigment. Moreover, themoisture absorptivity is significantly different between a pigment and apulp material. A pigment has a low moisture absorptivity compared with apulp material. Therefore, the variation rate V for coated paper isdifferent from that for plain paper.

In FIG. 6, the horizontal axis indicates the absolute moisture contentmeasured using the temperature and humidity sensor 40. The vertical axisindicates the variation rate V obtained based on the grammage when theabsolute moisture content is approximately 11.5 g/m³ (corresponding to atemperature of 25 C and a humidity of 50% RH). Here, the variation rateV for coated paper of 150 g/m² is shown as an example. Unlike thevariation rate V for plain paper shown in FIG. 4, the variation rate Vfor coated paper shown in FIG. 6 has a narrow width over which thevariation rate V varies and has a moderate slope. Similarly to the firstembodiment, it is possible to determine an approximation equation 2 forobtaining the variation rate V for coated paper from FIG. 6.variation rate V=0.01×moisture content g/m³+0.99  Approximation Equation2Note that hereinafter, the variation rate obtained from theapproximation equation 1 is denoted by V1 and the variation rateobtained from the approximation equation 2 is denoted by V2 in order todistinguish them.

Flowchart

A method for determining the type of the recording medium P in thecontrol unit 10 will be described with reference to FIG. 7. Note that inFIG. 7, descriptions of steps that are the same as steps described withreference to FIG. 5 are omitted for simplification. Note that in FIG. 7,step S502 is replaced by step S701, and steps S702 and S703 are addedafter step S505.

In step S701, the control unit 10 (the determination unit 24 and thecorrection unit 25) calculates the variation rates V1 and V2, which arecorrection coefficients for correcting a characteristic value (e.g.,grammage). For example, the control unit 10 may calculate the variationrates V1 and V2 by substituting the moisture content in theabove-described approximation equation 1 and approximation equation 2.Subsequently, steps S503 to S505 are executed, and the procedureadvances step S702.

In step S702, the control unit 10 (the determination unit 24) comparesthe dec value, which is a characteristic value, and a predeterminedswitching threshold, and determines whether or not the dec value issmaller than the predetermined switching threshold. The switchingthreshold is determined as follows, for example. In the secondembodiment as well, similarly to the first embodiment, a grammage of 115g/m² and 90 dec are in a corresponding relation. If the dec value isgreater than or equal to 90 dec, the grammage is less than or equal to115 g/m², and there is a high possibility that the recording medium P isplain paper. On the other hand, if the dec value is less than 90 dec,the grammage is greater than or equal to 115 g/m², and there is a highpossibility that the recording medium P is coated paper. Note that theswitching threshold (selection threshold for an approximation equation)is set to 90 dec, but this is merely an example. It is sufficient thatthe switching threshold is appropriately set in accordance with the typeof the recording medium P that is to be determined with priority in theimage forming apparatus 1. For example, in the case where it is desiredto give priority to detection accuracy for coated paper, the switchingthreshold may be set to 95 dec in order to more appropriately correct acharacteristic value for coated paper. In this manner, 5 dec may beadded as a margin in order to give priority to coated paper.Accordingly, the number of types of recording media P determined to becoated paper will increase, and the number of cases where coated paperis not determined to be coated paper decreases.

If it is determined in step S702 that the dec value is smaller than thepredetermined switching threshold, there is a high possibility that thetype of the recording medium P is coated paper, and thus the procedureadvances to step S703. In step S703, the correction unit 25 corrects thedec value, which is a characteristic value, using the variation rate V2for coated paper. On the other hand, if it is determined in step S702that the dec value is greater than or equal to the predeterminedswitching threshold, there is a high possibility that the type of therecording medium P is not coated paper, and thus the procedure advancesto the above-described step S506. In step S506, the correction unit 25corrects the dec value, which is a characteristic value, using thevariation rate V1 for plain paper.

In this manner, the correction unit 25 selects the variation rate V1 orV2 depending on the dec value, which is synonymous with selecting anapproximation equation. Accordingly, a characteristic value can beappropriately corrected depending on the dec value obtained from therecording medium P, and thereby the determination result for the type ofthe recording medium P will improve.

In this embodiment, plain paper and coated paper are described asexamples of the type of the recording medium P, but the technical ideaof the second embodiment is also applicable to any type of recordingmedium P. That is, the grammage of a recording medium P that has changeddue to the moisture content near the recording medium P is measured inadvance, and an approximation equation is obtained and stored in thecontrol unit 10. Furthermore, a switching threshold is set based on thegrammage of the recording medium P. This allows an appropriateapproximation equation to be selected in accordance with the type of therecording medium P, and thus detection accuracy for the recording mediumP will improve. The control unit 10 may be provided with anapproximation equation for the dec value in the case of thin paper whosegrammage is less than or equal to 70 g/m², as an example. If the decvalue is greater than or equal to 150 dec, there is a high possibilitythat the type of the recording medium P is thin paper. Therefore, thecorrection unit 25 corrects the dec value using the approximationequation for the dec value corresponding to thin paper so that thinpaper can be accurately determined.

In this manner, according to the second embodiment, an effect such asthe following will be obtained in addition to the effect of the firstembodiment. The determination apparatus 30 selects an approximationequation for the variation rate V in accordance with the type of therecording medium P (dec value). Thereby, detection accuracy for therecording medium P improves. For example, detection accuracy for therecording medium P can be improved for coated paper and thin papersimilarly to plain paper. Additionally, the image forming apparatus 1provided with the determination apparatus 30 sets an image formingcondition in accordance with the determined type of the recording mediumP, thereby achieving improvement in image quality. Here, description wasgiven regarding selecting the variation rate V1 or V2 and selecting theapproximation equation 1 or 2, which is equivalent to selecting orcorrecting a rule for determining a recording medium. Moreover, in thefirst and second embodiments, a characteristic value is corrected basedon a variation rate, but the threshold used in the step of determiningthe type of the recording medium executed in step S507 may be correctedor selected based on the variation rate.

As described in the first embodiment, in the second embodiment as well,the control unit 10 may control image forming conditions of the imageforming apparatus 1 directly based on the corrected dec value withoutdetermining the type of the recording medium P. Alternatively, imageforming conditions of the image forming apparatus 1 may be controlleddirectly based on the dec value and the corrected rule.

Third Embodiment

In the first and second embodiments, the type of the recording medium Pis determined using ultrasonic waves, but another method may be used. Amethod for determining the type of the recording medium P by irradiatingthe recording medium P with light and detecting reflection light fromthe recording medium P will be described below.

FIG. 8 is a block diagram showing an example of functions of thedetermination apparatus 30. The detection unit 23 has a light source 46,an imaging optical system 47 and an image capturing unit 48. The lightsource 46 is a light emitting element such as an LED. When the recordingmedium P is conveyed to the installation position of the detection unit23 at a certain speed, the control unit 10 instructs a light sourcecontrol unit 44 to start light irradiation. This instruction is an ONsignal meaning lighting of the light source 46, for example. Uponreceiving the instruction of irradiation start, the light source controlunit 44 generates a drive signal (drive current) and supplies the drivesignal to the light source 46 in order to light the light source 46. Thelight source 46 emits light in accordance with the drive signal from thelight source control unit 44 and irradiates the surface of the recordingmedium P with the light.

The light emitted from the light source 46 is reflected by the surfaceof the recording medium P. The imaging optical system 47 receives thereflection light from the surface of the recording medium P and focusesit on the image capturing unit 48. The image capturing unit 48 capturesthe light focused by the imaging optical system 47 (the surface of therecording medium P). The image obtained by the image capturing unit 48is an image of the surface of the recording medium P, and is output toan image processing unit 45. The surface of the recording medium P maybe positioned using a component such as a roller (not illustrated). Thisis performed in order to maintain the distance from the principal pointof the imaging optical system 47 to the surface of the recording mediumP at a certain distance, so that a focused image is obtained. Thesurface image obtained here changes depending on the surface property(roughness) of the recording medium P. The image processing unit 45obtains a characteristic value indicating the surface property of therecording medium P from a ratio of a shadow in the surface image, andoutputs an analog detection voltage corresponding to the characteristicvalue to the AD port of the control unit 10. Note that thecharacteristic value may be passed as a digital value to a digital portof the control unit 10. In this case, the image processing unit 45 maycalculate the dec value.

Similarly to the first embodiment, the AD port of the control unit 10converts the detection voltage indicating a characteristic value intothe dec value, which is a digital value. A parameter such as theresolution may be similar to that in the first embodiment. When the decvalue is determined, the control unit 10 instructs the light sourcecontrol unit 44 to stop irradiation. The control unit 10 obtains themoisture content using the temperature and humidity sensor 40.

Relation Between Surface Property and Type of Recording Medium P

In general, with a recording medium P having a smooth surface propertysuch as coated paper, the ratio of a shadow in the surface image issmall. Conversely, with a recording medium P having a rough surfaceproperty such as bond paper, the ratio of a shadow in the surface imageis large. In view of this, when the detection unit 23 detects arecording medium P with a smooth surface property, the AD port of thecontrol unit 10 performs requantization such that the dec value of thesurface property determined by the control unit 10 is 100 dec.Therefore, if the dec value is less than 100 dec, the determination unit24 determines that the type of the recording medium P is coated paper,and if the dec value is greater than or equal to 100 dec, determinesthat the type of the recording medium P is plain paper. Here, the typethreshold is 100 dec, but this is an example and an appropriate value isdetermined as the type threshold based on experiments or simulations.

Type of Recording Medium P and Image Forming Conditions

In general, the resistance value of a recording medium P having a smoothsurface property such as coated paper is low compared with theresistance value of a rough recording medium P such as bond paper.Therefore, the decision unit 26 sets a transfer condition (e.g.,transfer current) for transferring toner in accordance with the type ofthe recording medium P. Moreover, as for a recording medium P having asmooth surface property such as coated paper, a necessary fixingtemperature is low compared with a rough recording medium P such as bondpaper. This means that the time required for fixing is short. Thedecision unit 26 sets fixing conditions (fixing temperature, fixingtime, conveyance speed and the like) in accordance with the type of therecording medium P. If appropriate image forming conditions (transfercondition and fixing condition) are set in accordance with the type ofthe recording medium P in this manner, the image quality will improve.

Moisture Content and Image Forming Conditions

The resistance value and the surface property of the recording medium Pchange in accordance with the moisture content. Therefore, it isnecessary to set image forming conditions in accordance with themoisture content. Furthermore, change in the resistance value of therecording medium P that is in accordance with the moisture content isdifferent depending on the type of the recording medium P. Therefore,the decision unit 26 sets image forming conditions in accordance withthe type of the recording medium P and the moisture content, so as toform an appropriate image.

Influence of Moisture Content on Determination of Type of RecordingMedium P

The surface property changes according to the moisture content near therecording medium P. For example, if the moisture content near therecording medium P is large, the moisture content contained in fiberscomposing the recording medium P increases. Therefore, spaces betweenthe fibers are filled due to the expansion of the fibers, making thesurface smooth. On the other hand, if the moisture content is small, themoisture content in fibers composing the recording medium P decreases.Therefore, spaces between fibers expand, making the surface rough. In amethod for determining the type of the recording medium P based on thecharacteristic value of the surface property, determination error canarise depending on the magnitude of the moisture content. In some cases,the determination results are different between the case where the typeof the recording medium P is determined under an environment with aspecific moisture content envisioned in advance and the case where thetype of the recording medium P is determined under an environment with amoisture content different from the specific moisture content envisionedin advance. That is, in some cases, the determination results of therecording medium P differ between the case where the type of therecording medium P is determined based on the characteristic value ofthe surface property in an unchanged state and the case where the typeof the recording medium P is determined after the characteristic valueis converted into a characteristic value under an environment with aspecific moisture content.

In view of this, the determination unit 24 converts the characteristicvalue of the surface property into the characteristic value under aspecific environment and subsequently determines the type of therecording medium P, thereby achieving desired detection accuracy. In thethird embodiment, the specific environment (corresponding to atemperature of 25 C and a humidity of 50% RH) similar to those of thefirst and second embodiments is envisioned. In the third embodiment, themethod for obtaining the moisture content may also be the same as thoseof the first and second embodiments.

Relation Between Moisture Content and Characteristic Value

The influence that variation in moisture content detected by thetemperature and humidity sensor 40 has on the characteristic value ofthe surface property detected by the detection unit 23 will be describedwith reference to the inventors' experiment results shown in FIG. 9. Inthis embodiment, the absolute moisture content is used as an example inorder to estimate the moisture content contained in a recording mediumP. In FIG. 9, the horizontal axis indicates the absolute moisturecontent that is based on the detection result of the temperature andhumidity sensor 40. The vertical axis indicates the variation rate V ofthe characteristic value that is based on the above-describedcharacteristic value under the specific environment.

As described above, the characteristic value of the surface propertyincreases/decreases in accordance with increase/decrease in the moisturecontent. As shown in FIG. 9, the relation between the absolute moisturecontent near the recording medium P and the characteristic value isrepresented by a quadratic curve. Therefore, it is possible to calculatean approximation equation of the variation rate V based on FIG. 9. Ifthe absolute moisture content near the recording medium P can bedetected, the variation rate V is obtained using the approximationequation, and the characteristic value (dec value) is divided by thisvariation rate V, whereby the characteristic value under a specificenvironment is obtained. As an example, in an environment in which theabsolute moisture content is 24 g/m³, the characteristic value of arecording medium P shown in FIG. 9 is 0.96 times the characteristicvalue in the environment in which the absolute moisture content is 11.5g/m³. Therefore, in order to convert the characteristic value obtainedby the detection unit 23 into a characteristic value under a specificenvironment, it is sufficient that the correction unit 25 divides thecharacteristic value by 0.96. By dividing the characteristic value bythe variation rate V, the characteristic value is corrected to acharacteristic value under a specific environment. In the thirdembodiment, the determination unit 24 obtains the variation rate V ofthe characteristic value by substituting the absolute moisture contentnear the image forming apparatus 1 obtained by the temperature andhumidity sensor 40 in an approximation equation 3 obtained from thequadratic curve shown in FIG. 9.variation rate V=0.0002×(moisture content g/m³)²−0.01×moisture contentg/m³+1.08  Approximation Equation 3The approximation equation 3 of the variation rate V is an example inthe third embodiment, and is appropriately set in accordance with thedetection characteristic of the detection unit 23. Moreover, in thethird embodiment, the characteristic value is corrected based on themoisture content obtained from the detection result of the temperatureand humidity sensor 40. However, it is sufficient that a determinationresult of the type of the recording medium P that is in accordance withthe moisture content is obtained, and therefore the method of correctionis not limited thereto. For example, the target of correction does notneed to be the characteristic value and may be the type threshold thatis compared with the characteristic value in order to determine the typeof the recording medium P. The threshold is a threshold fordistinguishing between plain paper and coated paper, and an example ofthis threshold is 100 dec, for example. The correction unit 25 maycorrect the threshold of 100 dec based on the detected moisture content.Determination of the type of the recording medium P that is inaccordance with the moisture content without correcting thecharacteristic value is enabled by increasing/decreasing the thresholdin accordance with the moisture content. Moreover, as a method otherthan the method in which the characteristic value or the threshold iscorrected, a table indicating the relation between the moisture contentnear the recording medium P and the characteristic value may be storedin the storage unit of the control unit 10. By referring to the tablebased on the moisture content and the characteristic value, the type ofthe recording medium P is obtained. For example, a configuration may beadopted in which plain paper is identified from the table in the casewhere the characteristic value is 98 dec and the moisture content is11.5 g/m³, and coated paper is identified from the table in the casewhere the characteristic value is 98 dec and the moisture content is 5g/m³. In this manner, even in an environment in which it is determinedthat the recording medium (which is coated paper) is plain paper ifdetermination is performed using only the characteristic value, it canbe correctly determined that the recording medium is coated paper bytaking the moisture content into consideration. Note that description isgiven above regarding the moisture content in the first embodiment, andthus a redundant description is omitted here.

Flowchart

A method for determining the type of the recording medium P in thecontrol unit 10 will be described with reference to FIG. 10. Step S501is as described above. In step S1001, the control unit 10 (thedetermination unit 24, the correction unit 25) calculates the variationrate V, which is a correction coefficient for correcting thecharacteristic value (e.g., surface property). For example, the controlunit 10 may calculate the variation rate V by substituting the moisturecontent in the above-described approximation equation 3.

In step S1002, the control unit 10 starts light irradiation. Asdescribed above, the control unit 10 instructs the light source controlunit 44 to start the light irradiation. In step S1003, the control unit10 receive the light and obtains a characteristic value. For example,light reflected by the recording medium P is received by the imagecapturing unit 48, and a detection voltage is generated by the imageprocessing unit 45 and is input to the AD port of the control unit 10.The control unit 10 obtains a dec value, which is a characteristicvalue, by converting the analog detection voltage into a digital decvalue.

In step S1004, the control unit 10 stops the light irradiation. Asdescribed above, the control unit 10 instructs the light source controlunit 44 to stop the light irradiation. This may involve sending out anOFF signal to the light source control unit 44 or stopping the sendingout of an ON signal, for example.

In step S1005, the control unit 10 (the correction unit 25) corrects thecharacteristic value. For example, the correction unit 25 corrects thecharacteristic value based on the variation rate V. The correction isperformed using a function, a table, or the like in which the variationrate V and the characteristic value serve as inputs, and the correctedcharacteristic value serves as an output. For example, the function mayoutput the corrected characteristic value by dividing the dec value,which is the characteristic value, by the variation rate V.

In step S1006, the control unit 10 (the determination unit 24)determines the type of the recording medium using the correctedcharacteristic value. For example, the determination unit 24 comparesthe characteristic value and one or more thresholds and determines thetype of the recording medium. Subsequently, the procedure advances tostep S508.

According to the third embodiment, the determination apparatus 30corrects a characteristic value (e.g., surface property) of a recordingmedium P in accordance with the moisture content, and thus detectionaccuracy for the type of the recording medium P improves. Moreover, thecontrol unit 10 sets image forming conditions in accordance with thedetermined type of the recording medium P, and thus image quality willimprove. In this manner, in the third embodiment, the characteristicvalue is corrected based on the moisture content. However, it issufficient that the determination result for the type of the recordingmedium P that is in accordance with the moisture content is obtained,and thus the third embodiment is not limited only to a method in whichthe characteristic value is corrected. As an example of a method fordetermining an appropriate image forming condition, a table or the likeindicating the relation between the moisture content, the characteristicvalue and the image forming condition may be stored in the control unit10, and an image forming condition may be determined by referring to thetable based on the moisture content and the characteristic value. Inthis case, it will be possible to omit determination processing for thetype of the recording medium.

As described in the first and second embodiments, in the thirdembodiment as well, the control unit 10 may control image formingconditions of the image forming apparatus 1 directly based on thecorrected dec value without determining the type of the recording mediumP. Alternatively, the image forming conditions of the image formingapparatus 1 may be controlled directly based on the dec value and thecorrected rule.

Fourth Embodiment

In the third embodiment, description was given regarding correcting,based on a moisture content, the variation rate V of a characteristicvalue indicating the surface property of a recording medium P. Theapproximation equation described in the third embodiment may be switchedin accordance with the characteristic value of the recording medium P asdescribed in the second embodiment. As described above, the surfaceproperty of a recording medium changes in accordance with the moisturecontent contained in fibers. However, coated paper whose surface iscoated exhibits a tendency of the variation rate of a characteristicvalue to change, compared with plain paper.

The influence that the type of the recording medium P has on thecharacteristic value of the surface property will be described withreference to FIG. 11. Because the surface of coated paper has a pigmentapplied thereto, the coated paper has low moisture absorptivity comparedwith pulp material. Therefore, the variation rate V of the coated paperis different from the variation rate V of plain paper. In FIG. 11, thehorizontal axis indicates the absolute moisture content. The verticalaxis indicates the variation rate V based on the above-describedcharacteristic value of the surface property under a specificenvironment. Here, as an example, the variation rate V of the coatedpaper is shown.

The width over which the variation rate V of the coated paper variesshown in FIG. 11 is narrow compared with the width over which thevariation rate V of plain paper varies shown in FIG. 9. In view of this,an approximation equation 4 for obtaining the variation rate V of thecoated paper is obtained from FIG. 11. Here, the variation rate obtainedfrom the approximation equation 3 is denoted by V3, and the variationrate obtained from the approximation equation 4 is denoted by V4. Notethat the approximation equation 4 is also a quadratic function.variation rate V4=0.00005×(moisture content g/m³)²−0.01×moisture contentg/m³+1.03  Approximation Equation 4

Flowchart

A method for determining the type of the recording medium P in thecontrol unit 10 will be described with reference to FIG. 12. Step S501is as described above. In step S1201, the control unit 10 (thedetermination unit 24, the correction unit 25) calculates the variationrates V3 and V4, which are correction coefficients for correcting acharacteristic value (e.g., surface property). For example, the controlunit 10 may calculate the variation rate V3 by substituting the moisturecontent in the above-described approximation equation 3, and calculatethe variation rate V4 by substituting the moisture content in theapproximation equation 4. Subsequently, steps S1002 to step S1004 areexecuted and the procedure advances to step S1202.

In step S1202, the control unit 10 (the determination unit 24) comparesthe dec value, which is a characteristic value, and a predeterminedswitching threshold, and determines whether or not the dec value issmaller than the predetermined switching threshold. The switchingthreshold is determined as follows, for example.

Assume that the characteristic value of coated paper detected by thedetection unit 23 is 100 dec. In this case, if the characteristic valueis greater than or equal to 100 dec, the ratio of a shadow in thesurface image is large and there is a high possibility that therecording medium P is plain paper. On the other hand, if thecharacteristic value is smaller than 100 dec, the ratio of a shadow inthe surface image is small, and there is a high possibility that therecording medium P is coated paper. Here, it is assumed that theswitching threshold is 100 dec as an example. However, as described withrespect to the second embodiment, a margin may be added. For example, inthe case where it is desired to give priority to detection accuracy forcoated paper, the switching threshold may be 105 dec.

If it is determined in step S1202 that the dec value is smaller than thepredetermined switching threshold, there is a high possibility that therecording medium P is coated paper, and thus the procedure advances tostep S1203. In step S1203, the correction unit 25 corrects the decvalue, which is a characteristic value, using the variation rate V4 forcoated paper. On the other hand, if it is determined in step S1202 thatthe dec value is greater than or equal to the predetermined switchingthreshold, there is a high possibility that the recording medium P isnot coated paper, and thus the procedure advances to the above-describedstep S1005. In step S1005, the correction unit 25 corrects the decvalue, which is a characteristic value, using the variation rate V3 forplain paper. Subsequently, the procedure advances to step S1006.

In a fourth embodiment, plain paper and coated paper are determined astypes of recording media P, but these are merely examples. For anarbitrary type of recording medium P as well, an approximation equationis created in advance and a switching threshold is set, so that acharacteristic value can be appropriately corrected for an arbitrarytype of recording medium P as well. Note that the type threshold usedfor determining an arbitrary type of a recording medium P also needs tobe set in advance. For example, an approximation equation is created inadvance for bond paper, and the switching threshold is set to 150 dec.If the characteristic value is greater than or equal to 150 dec, thereis a high possibility that the recording medium P is bond paper.Therefore, the correction unit 25 selects an approximation equation forbond paper, and corrects the characteristic value. Accordingly, accuratedetermination for bond paper as well is enabled. In this manner, thedetermination unit 24 and the correction unit 25 function as a switchingunit or a selection unit for an approximation equation and variationrate.

According to the fourth embodiment, in addition to the effect of thethird embodiment, an effect such as the following can be obtained.Because the determination apparatus 30 selects an approximation equationin accordance with the characteristic value of the recording medium P,correction accuracy for the characteristic value will improve anddetection accuracy for the recording medium P will also improve. Forexample, detection accuracy for the type of the recording medium P forcoated paper and bond paper will improve similarly to plain paper. Theimage forming apparatus 1 provided with the determination apparatus 30can more appropriately set image forming conditions in accordance withthe type of the recording medium P, and thus image quality will improve.

As described in the first to third embodiments, regarding the fourthembodiment as well, the control unit 10 may control image formingconditions of the image forming apparatus 1 directly based on thecorrected dec value, without determining the type of the recordingmedium P. Alternatively, the image forming conditions of the imageforming apparatus 1 may be controlled directly based on the dec valueand the corrected rule.

Summary

As described with reference to FIG. 1, the determination apparatus 30has the detection unit 23, the measurement unit 22 and the determinationunit 24. The detection unit 23 detects a characteristic value indicatinga physical characteristic of a recording medium P. The measurement unit22 measures a moisture content that is correlated with the moisturecontent of the recording medium P. The determination unit 24 determinesthe type of the recording medium P based on the measured moisturecontent and the detected characteristic value. Furthermore, thedetermination unit 24 corrects the detected characteristic value usingthe measured moisture content, and determines the type of the recordingmedium P in accordance with the corrected characteristic value. In thismanner, according to this embodiment, because the moisture content ofthe recording medium is taken into consideration, detection accuracy forthe type of the recording medium improves. Note that the determinationunit 24 may correct a rule (e.g., threshold or table) for determiningthe type of the recording medium using the measured moisture content,and determine the type of the recording medium in accordance with thecorrected rule.

As described with reference to FIG. 1 and the like, the determinationunit 24 may have the correction unit 25 for correcting a characteristicvalue detected by the detection unit 23 using the moisture contentmeasured by the measurement unit 22. The correction unit 25 may have afunction or a table in which the moisture content measured by themeasurement unit 22 and the characteristic value detected by thedetection unit 23 serve as inputs and the characteristic value correctedin accordance with the input moisture content and characteristic valueserves as output. Such a function will be a function made by combiningthe above-described correction equation 1 and any of the approximationequations 1 to 4. Of course, such a function may be realized as a tableor the like.

The approximation equations 1 to 4 may be realized as a function or atable. These may be used for converting the characteristic valuedetected by the detection unit 23 into a characteristic value under apredetermined environment (e.g., temperature of 25 C and humidity of50%) based on the moisture content measured by the measurement unit 22.By converting the characteristic value detected by the detection unit 23into the characteristic value under the specific environment in thismanner, the influence of difference in environment can be reduced.

As described regarding the third and fourth embodiments, thedetermination unit 24 may function as a selection unit for selecting oneapproximation equation from among a plurality of approximation equationsin accordance with the characteristic value detected by the detectionunit 23. The approximation equation may be realized as a function or atable. Because correction accuracy for the characteristic value improvesby the correction unit 25 using an approximation equation selected bythe selection unit, detection accuracy for the type of the recordingmedium P will improve.

The above-described rule may involve determining the type of therecording medium by comparing the characteristic value detected by thedetection unit 23 and one or more thresholds. In this case, thedetermination unit 24 may have the correction unit 25 for correcting thethreshold in accordance with the moisture content measured by themeasurement unit 22. In this manner, a similar effect is also obtainedby correcting the type threshold without directly correcting thecharacteristic value. Furthermore, the correction unit 25 may have afunction or a table for inputting the moisture content measured by themeasurement unit 22 and outputting a threshold corrected in accordancewith the input moisture content. Note that a function or a table typefor obtaining the type threshold may also be determined by executingexperiments and simulation in advance at the time of designing theapparatus or shipping the apparatus from a factory.

As described regarding the first and second embodiments, thecharacteristic value of the recording medium P may be a value indicatingthe grammage of the recording medium P. If the grammage of the recordingmedium P changes, the electrical resistance value or the like alsochanges and thus the required transfer condition and fixing conditionchange accordingly. Therefore, a high-quality image is formed bydetermining an image forming condition suitable for the grammage.

As described with reference to FIG. 3, the detection unit 23 may havethe transmission unit 31 for transmitting ultrasonic waves to arecording medium, the reception unit 32 for receiving ultrasonic wavesthat were transmitted from the transmission unit 31 and passed throughthe recording medium, the reception detection unit 43, and the AD port.The reception detection unit 43 and the AD port output a characteristicvalue that is in accordance with the amplitude value of the receptionsignal output by the reception unit 32 upon receiving the ultrasonicwaves. In this manner, the grammage can be more accurately detected byusing ultrasonic waves. Moreover, information regarding the grammageincludes the thickness of the recording medium P. The larger thethickness of the recording medium P is, the larger the grammage of therecording medium P is, if the recording medium P is composed of the samematerial. The method for detecting the thickness includes a method inwhich light is emitted and the transmittance of the light is measured.Here, as described regarding the third and fourth embodiments, if themoisture content contained in the recording medium P changes, spacesbetween the fibers composing the recording medium P change. As a result,the transmittance of light changes. Therefore, in a configuration fordetecting the thickness of such a recording medium P as well, a highquality image can be formed by applying the present invention. However,if an optical system for emitting light or a light receiving system isdirtied by paper dust, erroneous detection occurs. However, thetransmission unit 31 and the reception unit 32 for ultrasonic waves areunlikely to be influenced by paper dust.

As described regarding the third and fourth embodiments, thecharacteristic value of the recording medium P may be a value indicatingthe surface property of the recording medium P. The appropriate imageforming condition differs depending on the surface property of therecording medium. Therefore, the type is identified in accordance withthe surface property of the recording medium P, an image formingcondition that is in accordance with the type is set, and thereby thequality of the image improves.

As described with reference to FIG. 8, the detection unit 23 may beprovided with the light source 46 for irradiating a recording mediumwith light, the image capturing unit 48 for receiving the lightirradiated from the light source 46 and reflected by the recordingmedium P, the image processing unit 45, and the AD port. The imageprocessing unit 45 and the AD port function as a signal processing unitfor outputting a characteristic value that is in accordance with a lightreceiving signal output by the image capturing unit 48 upon receivingthe light. Accordingly, the characteristic value indicating the surfaceproperty of the recording medium P can be obtained.

The measurement unit 22 may be provided on a conveyance path for therecording medium P, in a housing unit for accommodating the recordingmedium P, or around them. As described with reference to FIG. 2, it issufficient that the moisture content near the recording medium P can bemeasured in order to measure a moisture content that is correlated withthe moisture content of the recording medium P. Therefore, theconveyance path and the feeding cassette 2 for the recording medium Pwill be appropriate as a position for measuring the moisture contentnear the recording medium P. Note that the measurement unit 22 isprovided at a position that is away from a heat source by apredetermined distance or more. Change in temperature near a heat sourcesuch as the fixing apparatus 20 or a motor is significant, and thuserroneous measurement of the moisture content of the recording medium Pis likely to occur. Therefore, the measurement result of the moisturecontent improves by providing the measurement unit 22 at a position thatis separated from a heat source by a predetermined distance or more. Itis sufficient that the distance from the heat source is determined inadvance by executing experiments or simulation at the time of designingthe apparatus or shipping the apparatus from a factory.

The measurement unit 22 may have the temperature and humidity sensor 40for detecting a temperature and a humidity and a calculation unit forobtaining a moisture content from the temperature and the humiditydetected by the temperature and humidity sensor 40. Such calculationunit may be implemented in the control unit 10.

As described above, the image forming apparatus 1 may have thedetermination apparatus 30, the decision unit 26 for determining animage forming condition corresponding to a determined type of arecording medium, and the image forming unit 50 for forming an image onthe recording medium using the determined image forming condition. Thedetermination apparatus 30 of this embodiment can accurately determinethe type of the recording medium P by taking the moisture content intoconsideration, and thus an image forming condition determined inaccordance with the type of the recording medium P will be appropriate.Accordingly, the quality of the image (e.g., gradation reproducibility,color reproducibility and the like of an original image) will improve.

The image forming conditions include at least one from among a transfervoltage, a transfer current, a fixing temperature and a conveyance speedregarding a recording medium P. These parameters are parameters that areto be changed in accordance with the grammage and the surface property,and therefore receives benefits of this embodiment.

The image forming conditions may include a discharge amount of ink. Theimage forming unit 50 was described as forming an image in accordancewith the electrophotographic process, but the image forming unit 50 thatuses an ink jet recording method may be adopted. The rate of absorptionof ink is also influenced by the grammage and the surface property.Therefore, a more appropriate discharge amount of ink is determined byaccurately obtaining the characteristic value of the recording medium Pand accurately determining the type. Accordingly, overflow of ink or thelike will be reduced.

In these embodiments, description was given with a focus on correcting acharacteristic value, but the characteristic value does not need to bedirectly corrected. For example, an appropriate image forming conditioncorresponding to the combination of a characteristic value and amoisture content may be determined in advance, and an image formingcondition corresponding to the combination of a detected characteristicvalue and a measured moisture content may be determined by the decisionunit 26. In this case, the characteristic value may be the grammageonly, the surface property only, or both of them. In this manner, thecombination of a characteristic value and the moisture contentcorresponds to a corrected characteristic value, and thus such adetermination method actually involves the corrected characteristicvalue. This is because when determining an image forming condition, thecharacteristic value is corrected and the type is determined in advance,and the image forming condition is determined based on the type. Thedecision unit 26 may be provided with a table storing the relationbetween the combination of a characteristic value and a moisture contentand the image forming condition corresponding thereto. The decision unit26 refers to the table based on the combination of a detected ormeasured characteristic value and moisture content and selects ordetermines an image forming condition corresponding to the combination.

The measurement unit 22 does not necessarily need to be provided on theconveyance path. As shown in FIG. 13, the measurement unit 22 may beprovided near a fan 60 that takes in outside air and cools the inside ofthe image forming apparatus 1. Accordingly, the measurement unit 22 canmeasure substantially the same values as those of the temperature andthe humidity outside of the image forming apparatus 1. The fan 60 may beeither an intake type cooling fan or an exhaust type cooling fan. Inthis manner, the measurement unit 22 may be arranged at a positionseparated from the determination apparatus 30 as long as thetemperature, the humidity or the like around the recording medium P canbe measured. Note that in the case where an exhaust type cooling fan isadopted, the measurement unit 22 may be arranged around the inlet port.In this manner, the measurement unit 22 may be arranged in some place ona flow passage of the outside air. Moreover, the measurement unit 22 maybe provided on the exterior casing of the image forming apparatus 1. Thetemperature and the humidity of the recording medium P are basicallycorrelated with the temperature and the humidity of the outside air.Therefore, the moisture content of the recording medium P is alsocorrelated with the moisture content of the outside air. Therefore, ifthe moisture content of the outside air can be measured, it will bepossible to accurately estimate the moisture content of the recordingmedium P.

Moreover, in the above-mentioned embodiments, a configuration is adoptedin which the determination apparatus 30 is provided so as to be fixed tothe image forming apparatus 1, but a configuration may be adopted inwhich the determination apparatus 30 is detachable from the imageforming apparatus 1. If the determination apparatus 30 is configured tobe detachable, a user can easily replace the determination apparatus 30if it has a failure, for example. Alternatively, in the case of updatingor adding a function of the determination apparatus 30, a user caneasily exchange the sensor thereof for a sensor having the new function.Moreover, a configuration may be adopted in which the determinationapparatus 30 can be simply mounted on the image forming apparatus 1 asan addition.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-240367 filed Nov. 27, 2014 which is hereby incorporated byreference wherein in its entirety.

What is claimed is:
 1. An apparatus for determining a type of arecording medium, comprising: a detection unit including: a transmissionunit configured to transmit ultrasonic waves toward the recordingmedium, and a reception unit configured to receive ultrasonic waves thatwere transmitted from the transmission unit and passed through therecording medium, the detection unit configured to detect acharacteristic value indicating a physical characteristic of a recordingmedium; a measurement unit configured to measure information regarding amoisture content contained in the recording medium; and a control unitconfigured to determine the type of the recording medium by reducing aninfluence of an amount of moisture content contained in the recordingmedium from the characteristic value based on the information regardingthe moisture content and the characteristic value.
 2. The apparatusaccording to claim 1, wherein the detection unit detects thecharacteristic value indicating a grammage of the recording medium. 3.The apparatus according to claim 2, further comprising: a signalprocessing unit configured to output the characteristic value that is inaccordance with an amplitude value of a reception signal output by thereception unit upon receiving the ultrasonic waves.
 4. The apparatusaccording to claim 2, wherein the control unit is further configured to:in a case where it is determined, based on the information measured bythe measurement unit, that the moisture content contained in therecording medium is more than a predetermined amount, correct thecharacteristic value detected by the detection unit such that thegrammage of the recording medium is reduced, and in a case where it isdetermined, based on the information measured by the measurement unit,that the moisture content contained in the recording medium is less thanor equal to the predetermined amount, correct the characteristic valuedetected by the detection unit such that the grammage of the recordingmedium is increased.
 5. The apparatus according to claim 1, furthercomprising: a correction unit configured to correct one or morethreshold values for determining the type of the recording medium usingthe information measured by the measurement unit, and wherein thecontrol unit determines the type of the recording medium by comparingthe characteristic value detected by the detection unit and the one ormore threshold values corrected by the correction unit.
 6. The apparatusaccording to claim 1, wherein the measurement unit includes: a sensorconfigured to detect a temperature and a humidity, and wherein themeasurement unit obtains a moisture content of a space around therecording medium based on the temperature and the humidity detected bythe sensor.
 7. The apparatus according to claim 6, wherein the sensor isprovided in a periphery of a conveyance path for the recording medium ora housing unit configured to accommodate the recording medium.
 8. Theapparatus according to claim 6, further comprising: an intake type orexhaust type cooling unit, wherein the sensor is provided in a peripheryof the cooling unit.
 9. The apparatus according to claim 6, wherein thesensor is provided at a position separated from a heat source by apredetermined distance or more.
 10. An image forming apparatuscomprising: an image forming unit configured to form an image; adetection unit including: a transmission unit configured to transmitultrasonic waves toward the recording medium, and a reception unitconfigured to receive ultrasonic waves that were transmitted from thetransmission unit and passed through the recording medium, the detectionunit being configured to detect a characteristic value indicating aphysical characteristic of a recording medium; a measurement unitconfigured to measure information regarding a moisture content containedin the recording medium; and a control unit configured to control animage forming condition of the image forming unit, wherein the controlunit is configured to control the image forming condition by reducing aninfluence of an amount of moisture content contained in the recordingmedium from the characteristic value based on the information regardingthe moisture content and the characteristic value.